Measured-service telephone system



QC@ z3, 192s. 1,688,617

R. W. ENGSBERG MEASURED SERVICE TELEPHONE SYSTEM Filed April 18, 1925 i.. Y v 0 THEKJLJ 7'0 BUSY 70N alfh M En aber@ .HTT-

Patented Got. 23, 1928.

UNITED STATES PATENT OFFICE. y

RALPH W. ENGSBEBG, 0F OAK PARK, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS,

TO AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATIONlOIi DELA- WARE.

Application filed April 18, 1925 The present invention relates in general to measured service telephone systems, but is particularly concerned with such systems when they are provided with both primary and secondary line switches; and the primary object of the invention is to reduce the cost of an installation of this kind by reducing the .amount of equipment heretofore considered necessary.

In a typical trunking system of this chai'- acter, using ten percent trunking, there are ordinarily provided ten secondary line switches for each one hundred subscribers lines, and ten first selectors for each twentyfive secondary line switches. As is well known the purpose of these secondary line switches is to enable the use of larger trunk groups. which are known to be more eflicient than a large number of small trunk groups.

In a measured service telephone system, using secondary line switches it has heretofore been the practice to provide a pair of meter control relays in each trunk extending from the bank contacts of the primary line switch, and to also provide a number of chain relays, one for each trunk extending from the bank contacts of the secondary line switches to the first selectors. These chain relays render means effective when all the trunks eX- tending to the first selectors are busy, to complete an operating circuit for a gang relay which in turn operates to make all secondary switches not in use, having access to this particular selector group, busy to all primary line switches.

It will be seen from this that, for each 100 lines in a system using ten percent trunking as above outlined, there will be ten sets or twenty meter control relays for each 100 lines, and ten chain relays, making a total of thirty relays.

Now, in accordance with applicants invention, a single meter control relay is placed in each first selector. This relay is arranged to function not only as a meter control relay, but also as a substitute for the usually provided chain relay, and since there are only ten trunks extending to each first selector group, these ten relays take the place of the thirty relays formerly required. It will be appreciated from this that in a large system the resulting saving in equipment as well as space will be appreciable.

MEASURED-SERVICE TELEPHONE SYSTEM.

Serial No. 24,034.

In order to aid in the description of the invention the same has been illustrated and described as being incorporated ina well known type of telephone system. So much of this system as is necessary for a clear understanding of the invention is shown in the figure of drawing forming a part of this specification.

In the drawing the substation A consists of the usual equipment found in substations of automatic telephone systems. The line switch C is of the well knownplunger type, and is always maintained in front of an idle trunk by the master switch E. The secondary line switch D is of the well known continuous rotary type. The selector F is of the well known vertical and rotary type. The purpose of the various relays and other equipment shown in the upperright hand corner of the drawing and the associated circuits will be clearly explained and described hereinafter.

Having briefly described the apparatus involved, its operation will now be described in detail with a View to pointing out the particular features of novelty disclosed. v For this purpose it will be assumed that the subscriber at substation A desires to call some other subscriber in the system, and the operation of the primary and secondary line switches C and D, and the operation of the first selector F in connecting the line of substation A to a desired trunk group, will be described. l

When the receiver at substation A is removed a circuit is completed over the line conductors 11 and 12 from battery, winding of line relay 16, resting contact and spring 20, line conductor 11 extending to and through the substation apparatus, line conductor 12, spring 22 and its resting contact, common conductor to ground through the low resist'- ance winding of supervisory relay 129. Upon energizing, the line relay 16 at armature 25 closes a circuit for the pull-down winding 18 of the line switch C. The pull-down windin turn operates both the cut-off armature 21 and the plunger arm 21` the former being effective to disconnect the line conductors 11 and 12 from the. winding of the line relay and ground, respectively, while the latter forces the bank springs 30, 32, 31, 33, into engagement with contacts 34, 36, 35, and 37, respectively. By the engagement of bank springs 30 and 33 with contacts 84 and 87, the line conductors 11 and 12 are extended by way of armatures 56 and 59 and their back contacts to the winding of line relay 50 and ground, respectively, at the secondary switch D. A circuit including the calling line is accordingly completed for the line relay 50. This relay, upon operating, at its armature 19 completes a holding circuit for the line switch C, the circuit being traceable from grounded front Contact and armature 19, springs controlled by armature 58, bank contact 85, bank spring 31, and, the holding` winding 17 of the line switch C, to battery. This holding circuit is established before the slow acting line relay 16 of the line switch C has had time to deenergize and is effective to retain the plunger arm 21 and the cut-oil1 armature 21 in operated position. A ground potential is also placed on the private normal conductor 135,

which is connected with the multiple test contacts of the banks of the connectors which have access to the line of substation A, thereby guarding the lme against intrusion in the usual manner.

As a result of the application of ground to bank contact 35, ground is also supplied to the corresponding test contact in the bank of the master switch E by way of conductor 149, thereby completing a circuit for starting` relay 127 of the master switch by way of the master switch test wiper 107. Relay 127 is accordingly energized to complete a circuit for locking relay 151. As is well understood, when the locking relay is energized it releases the master switch shaft (controlling the. idle line switchy plungers) and the shaft instantly turns in a counter-clockwise direction under control of a governor, the operating force being supplied by a heavy spring under tension.. The test wiper 107 is attached to this shaft, from which it will appear that this wiper' will disengage the associated test contact and come into engagement with the ninth test contact. Assuming that this ninth test contact is idle, in which case there will be .no ground potential present, the starting relay 127 will deenergize in turn causing the locking relay to also restore to stop the master switch with the plungers of all idle. line switches before the ninth idle trunk.

It may also be pointed out that when the locking relay 151 is energized it closes a circuit for the open main Yrelay 134 which operates to disconnect the common .conductor 44 from the nongrounded pole of the battery. This is to prevent the operation of any other line switches of the group while the master switch shaft is being moved from one trunk to another by the master switch..

Continuing now with the operation of the secondary line switch D the line relay 50, in addition to applying ground back to the line switch, master switch and line normals as hereinbefore explained, at its armature 40 applies ground to one terminal of the switching relay 51, thereby completing a circuit. for this relay in series with the rotary magnet 52, and, at the same time by means of armature 55, connects thetest wiper 41 to, this circuit at a point midway between the relay 51 and the magnet. The operation now depends upon whether the trunk line with which the wiper 41 is in engagement is busy or idle. lf the trunk line is busy, there will be a ground potential on. the test contact engaged thereby, resulting in the switching relay 51 being short circuited. The stepping magnet 52 which interrupts its own circuit will now operate in the manner of a buzzer to advance the switch wipers step byl step until an idle trunk is found. Vhen the wipers arrive at an idle trunk line, which we will assume is the trunk line extending to the selector F, the test wiper 41 will find no ground potential on the test contact 42, and the rotation of the switch will cease. The switching relay 51, being no longer short circuited, will now energize in series with the stepping magnet 52, the latter magnet remaining inoperative on account of the high resistance of the switching relay. Relay 51, upon energizing, at armature 58 connects the incoming release trunk conductor 43 to the test wiper 41, and

at its armature 57 and its working Contact e locks itself .to the grounded conductor 43 which extends back to the line switch C. Ground, at the working contact and armature 19 of the line relay 50 is maintained on the test wiper 41 until after a holding Acircuit from the seized selector F has been established. ln addition to the foregoing, relay 51, at its armatures 55 and 59, disconnects the incoming'trunk conductors from thewinding of line relay 50 and from ground, respectively, and extends them by way of wipers 146 and 147, bank contacts 71 and 7 3, conductors 7 7 and 79, to the line relay 68 of the selector l?, the conductor 79 extending by way of armature 92 and its resting contact, and the conductor 77 extending by wayl of the upper winding of relay 80 and armature 91 and its resting contact. Y

Line relay 68 energizes over the circuit of the calling line, and in'turn completes 'an energizing circuit for slow release relay 75. rllhis latter relay, upon operating, at its armature 82 opens one point in a multiple ground holding circuit of trunk busy relay 106, and at the front Contact of this armature places a ground potential upon the release conductor 48', thereby establishing` a holding circuit lll and at the front contact of this armature prepares a circuit for the vertical magnet 85 and the series relay 84.

ln addition to the above the slow release relay 7 5 at its armature 82 also supplies ground to the lower winding of relay 8O via the resistance element 141. Relay does not operate, however, at this time as the windings are so proportioned that the upper winding of this relay is not strong enough to operate the same alone, nor will the relay operate when the lower winding is also energized by current flow in the opposite direction through the resistance element 141. lf, however, the current is reversed in the upper winding orl it ground potential is applied directly to the lower winding this relay operates.

The calling subscriber at substation A may now proceed to operate the impulse transmitting device S to transmit a detinite number of impulses or breaks in the line circuit, causing a corresponding number ot deenergizations ot relay 68 in the usual manner. This results in a corresponding number ot impulses being transmitted from the grounded back contact ot armature 89, armature 69 and its back Contact, armature 83 and its working contact, win ding ot relay 84, and the winding of magnet 85 to battery. Since the relay 84 is slow to release it remains energized throughout the series of impulses. The vertical magnet 85, however, responds to each impulse to cause the wipers 143-145, inclusive, to be elevated opposite a desired group of trunks. T he switch, upon taking its first vertical step` operates its oil normal springs 98, 99 and 100. Spring 100, upon engaging its working contact, completes a circuit tor the stepping relay 95, this circuit being traceable trom grounded armature 82 and its working contact, working cont-act and armature 8G. oli normal spring 199 and its working contact, and the winding of stepping relay to battery. Relay 95 at'its armature 96 completes a locking circuit for itself independent ot the armature 86 of relay 84, the circuit extending -from grounded baclr contact and arn'iaturc 89, working Contact and armature 9G, interrupter springs 93 on the rotary magnet 128., and the oil normal spring and its working contact. As a result of the oli normal spring 99 engaging its working contact, a point is closed in the circuit ot release magnet 142. This circuit, however, is ineffective at this time due to its circuit being open at armature 83 ot slow release relay 75.

Shortly following the transmission of the first series of impulses, slow release relay 84 doenergizes, and in so doing, completes a circuit for the rotary magnet 128, the circuit being` traceable from grounded armature 82 and its working contact, springs controlled by arnizaure armature 97 and its working contact and the winding of rotary magnet 128 to battery. ilagnet 128 operates to step the wipers of the selector into engagement with the first bank Contact of the group selected. As a result of the energization of rotary magnet- 128 the previously described circuit for stepping relay 95 is broken at springs 98, resulting in the deenergization ot the stepping relay. The operation from this point on, that is the selection of an idle trunlr, is dependent on the nongrounded or grounded condition of the test Contact, lf the first trunlr line engaged is busy ground will be present on the test contact 117, and a circuit will again be completed by way of wiper 144, armature 99 and its resting contact, interrupt-er springs 98, olf normal spring 100 and the winding of relay 95 to battery. As a result the stepping relay will again operate to complete the circuit for rotary magnet 128. The alternate operation of magnet 128 and relay 95 is continued until the wiper 144 engages a test Contact associated with an idle trunk line. When this occurs the stepping relay is not again energized, but instead switching relay 8'?, which has heretofore been short circuited by ground on the test wiper, is now operated in series with the stepping relay 95. Owing to the comparative high resistance ot switching relay 8.7 relay 95, however, is not energized at 'this time'. llelay 87, however, operates and at its armatures 91 and 92 disconnects the line relay 68 from connection with the calling line and extends the calling line to the line conductors of the selected trunk via the wipers 143 and and their associated bank contacts. Relay 8T also at its armature 90 and its trent contact prepares a circuit for maintaining ground on the release conductor 48', after the deenergization or' relay 75, which takes place shortly following the deenergization of line relay 68. At armature 89 ground is removed from connection with-armature (i9 ot the line relay so that upon the deenergization of t-he relays 68 and 75 no circuit is completed for release magnet 142.

rlhe remainder of the operations in which the calling subscriber controls the remaining ot a plurality of other automatic switches through the medium of his calling device Si to complete the vconnection to the desired line, are well understood, and these operations will not be further considered except to point out that the connector used is ot the type which reverses tlc direction of current liow in the calling line upon response of the called subscriber, and that when the subscribers have finished talking the restoration of the calling subscribers receiver to the switchhoolr causes the automatic switches to restore to normal with 'the result that ground is dis connected from the release trunlr conductor .3. rlhis operation breaks the holding circuit or the primary and secondary line switches C and D and these switches are restored to normal. v

As previously mentioned, the connector used is of the type which, when the called subscriber' answers, reverses battery back to the calling line. lllhen this occurs the electropolarized relay 80 in the selector l? operates, at its armature 104 and its working contact shunts out theupper winding of relay 80 to improve the talking path, at armature 103 applies ground to the conductor 7S to operate the calling` subscribers meter over a circuit eX- tending back through wiper 148, workco-ntact and armature 150, bank contact 3th bank spring 32, and the winding of meter M to battery, causing the meter to operate to charge for the connection,

As previously pointed out it is necessary to make all trunk lines incoming to group or" secondary line switches busy whenever all of the trunk lines outgoing from such secondary group `become busy. 'lhe arrangement vfor accomplishing this consists of a trunk group busying relay 100 which is normally maintained energized by multiple ground leads, there being one such lead eX- tending to each selector oi' the group.

IThe complete circuit of one such conductor is shown in the drawing. rllhis circuit extends from the grounded armature 82 ot relay 75 and its resting contact, ott normal spring` 9S and its resting contact, armature 102 and its resting contact, conductor 152, and the winding` ot relay 100 to battery.

We will assume that when selector lF was seized it was the last idle selector of the group. Under these conditions, upon energization of relay 75 the last ground connection extending to relay 106 is broken. Relay 106 immediately restores, at its armature 107 completes an operating circuit for the all-trunk-busy meter M2, at its armature 108 breaks the normally completed circuit for relays 85 and 112, and at its armature 109 momentarily completes a circuit for the supervisory lamp L and relay 111. Upon deenergization of slow release relay 112, and as a result of the deenergization of relay 85', ground at armatures 105 is applied to all the bank contacts connected with secondary switches ol the group not in use so that the master switch will keep all idle primary line switch plungers before trunk lines having access to secondary line switches having access to some other selector group in which all trunks are not busy.

Relay 111, upon operating, applies ground to the operating conductor 94 ot each ot the primary master switches, thereby completing a circuit for relay 102 in each switch. Upon energizing, relay 102 establishes a locking circuit for itself at its armature 130, and at its armature 131 closes the circuit of the lockingrclay 151. Upon energizing, relay 151 closes a circuit for the open main relay 134 and at the same time unlocks the master switch shaft mechanically so that it is Yfree to move to the left or in a counterclockwise direction, under control of its main spring and governor, as previouslyexplained. Since relay 102 is locked up independent of conductor 94, this movement of the master switch shaft will continue until wiper 10'? arrives at its first test contactat which time the line switch plungers will be opposite the lirst trunk. The arm 122 now closes contact springs 124 and 125, thereby completing a circuit for relay 104. lVhcn relay 104 attracts its armature the armature is locked in operated position behind the tooth on spring.

126 so that the relay remains in operated position after the energizing circuit is broken. T he enerofization of relay 104 breaks the locking circuit or' relay 102, permitting this relay to fall back, and also closes a new circuit 'for the locking relay 151, in order that this latter relay may be held up after relay. 102 has deenergized. Relay 104 also closes a circuit for the solenoid 105. Upon energization of the solenoid, the master switch shaft is rotated by a-continuous movement in a clockwise direction until all the plungers are lined up opposite thetcnth trunk, wiper 107 being restored to the position shown in the drawing. Arm 123 now disengages spring 126 from the armature of relay 104 and this armature is released to break the circuit of the solenoid 10G and the circuit of relay 151. Relay 151 now deenergizes and locks the shaftfin position opposite the tenth trunk. Obviously, when the primary master switches are operated, any line switch plungers which happen to be disengaged from the shaft are picked up and are again brought under control of the master switch so that there will be no danger oi any of them being plunged in on busy trunk lines.

lt is possible for a subscriber to operate his primary line switch after all trunks leading 'trom the .secondary line switch to which his primar line switch has access, only in a remote case if all mechanisms are in proper operating condition. lThis may be accomplishcd in the interval between the deenergization of relay 106 and the energization of open main relay 134. Even though the chances or' this happenino` are very few, precautions have been taken to make sure that a connection is established no further than the primary line switch. lt will be noted that at armature 111 of relay 106 the normal shunt circuit around relay 114 is removed by the deenergization of relay 106, placing high resistance relay 114 in series circuit with the line relay of the secondary line switch. 'llhereform a subscriber who has succeeded in operating his primary line switch can proceed no further because the line relay of the secon( ary line switch will not energize in series with relay 114. However, relay 114 will operate to operate the overiiow meter M3. A busy tone is substituted for direct ground on conductor 12 at armature 111. This busy tone is to notify the subscriber that all the trunlrs in that secondary group are busy and that the call can be extended no further.

Another point ot' operation which may be pointed out at this time is the arrangement for enabling the selector switch F to be made busy in case of trouble. This may be accomplished by simply inserting a metal object between the test jack springs 140 which will result in the relay 80 operating, since this `circuit excludes the resistance element 141. At this time, since the switch is at normal, ground is removed from the common conductor extending to relay 106 by the operation ot armature 102', and at armature 101 ground is connected to the release conductor 423 so as to prevent this trunlr being seized by a secondary line switch which may be seeking for an idle trunlr.

What is claimed is:

1. In a telephone system, a calling line, a meter for said line, selector switches, primary and secondary trunlring switches responsive to the initiation of a call to extend a connection to an idle one of said sel ctor switches, other switches, means for operating a seized selector and said other switches to complete a connection, a plurality of relays, there being one in each selector switch operated when the selector is seized, means common to said selector switches responsive to the joint operation of all said relays to prevent the operation of idle secondary trunlring switches, and means common to said trunking switches for causing the operation of the said meter upon completion of a connection. n

2. In a telephone system, calling lines equipped with meters, a group ofk primary trunk hunting switches for said lines, a smaller group of trunk hunting switches accessible to said primary switches, a group et selectors accessible to said last group of trunk hunting switches, means common to all the switches operative in response to the seizure of the last idle selector switch of the group to render all idle secondary switches inoperative, and means common to the primary and secondary switches operative upon completion of talking connections for causing the meters of the lines calling to be operated.`

3. In a telephone system, a calling line, a meter for said line, means including primary and secondary trunk hunting andselector switches for setting up connections to called lines, means common to said trunk hunting switches responsive when all selector switches have beentaken for use to render all of the idle secondary switches busy, and means in each of the selectors operative upon response of the subscriber called to effect the operation of the calling lines meter.

4. In a measured service telephone system, primary and secondary non-numerical trunk hunting switches, selector switches accessible to said primary switches via said secondary switches, a normally energized relay operative to make all idle secondary switches busy to said primary switches whenever all selectors are in use, and circuit connections eX- tending to all selectors as long as they are idle for holding said relay energized to prevent its operation. i

5. In a measured service telephone systern, primary and secondary trunk hunting switches, numerical switches accessible to said primary switches via said secondary switches, a meter, a normally energized relay directly controlling said meter and common to said numerical switches, operative when the last one of a group of said numerical switches are taken for use to render all idle secondary switches busy to other incoming calls and register said condition on said meter, and means in said numerical switches when all or any are idle for maintaining said relay energized.

6. In a measured service telephone system, primary and secondary trunk hunting switches, selector switches accessible to said primary switches via said secondary switches, a meter, a normally energized relay directly controlling said meter and common to said selector switches, and operative to render all idle secondary switches busy to said primary switches whenever all selectors are in use, and means in said selectors for preventing t ie operation of said relay and meter, as long as any of said selectors are idle by maintaining said relay energized; Y

7 In a measured service telephone systeni, primary and secondary trunk hunting switches, selector switches accessible to said primary switches via said secondary switches, a meter, a relay directly controlling said meter and operative when all selectors are in use to make all idle secondary switches busy and register all trunks busy condition. a second meter, a second relay controlling said second meter and operative when said iirst relay operates, to register lost calls, and acting as a means to prevent a seized secondary lswitch from operating.

In witness whereof, I hereunto subscribe my name this 16th day of April, A. D., 1925.

RALPH W. ENGSBERG. 

